Structure for and method of surface condition sensing and indicating and motor speed control

ABSTRACT

The condition of a surface is sensed by cyclically moving two members having engaged surfaces relative to each other, driving the surfaces for only a portion of each cycle to set up a threshold kinetic energy level in accordance with the friction between the engaged surfaces, sensing the kinetic energy developed in one of the members due to moving the members relative to each other, comparing the developed kinetic energy with the threshold kinetic energy and controlling the cyclic movement of the members in accordance with the relationship between the kinetic energy threshold and the developed kinetic energy. The cyclic movement of the members is then used to provide a visual indication of the condition of one of the surfaces. The structure for surface condition sensing and indicating includes a pair of cyclically relatively movable members in surface-to-surface frictional engagement, means for driving the members relatively for a portion of a cycle of relative movement thereof, means preventing driving of the members for the rest of the cycle of relative movement thereof to establish a threshold of kinetic energy in one of the members necessary to maintain relative movement between the members during the portion of the cycle in which they are not driven relatively, means to sense the relation between the kinetic energy of the one of said members relative to the threshold kinetic energy established, means for varying the time between cycles of driving the members relatively in accordance with the relation between the established threshold of kinetic energy and the sensed kinetic energy of the one member and means for providing a visual indication of the relation between the kinetic energies. The means for controlling the cycle time includes means for immediately starting a new cycle of operation if the sensed kinetic energy is greater than the threshold kinetic energy established and for providing a predetermined dwell time between cycles of relative movement of the members if the sensed kinetic energy level is below the established kinetic energy level. Structure is also disclosed for varying the dwell time in accordance with the exact proportion between the established kinetic energy level and the sensed kinetic energy level in conjunction with particular structure for developing an electric signal proportional to speed of an electric motor. The particular structure for developing a signal proportional to motor speed includes one or more additional commutator brushes provided in conjuction with the motor through which a signal is developed from the motor proportional to motor speed. The particular structure for developing a signal proportional to motor speed is also disclosed in conjunction with a method of and means for motor speed control. The method of motor speed control includes driving an electric motor with an electric signal, taking an electric signal from the motor itself proportional to motor speed and controlling the signal electric siganl with the signal proportional to motor speed. The structure disclosed for controlling the speed of a motor includes a source of reference electric signal high gain structure for feeding electric energy to the motor, the particular structure including a third commutator brush on the motor for developing an electrical signal proportional to the speed of the motor, means for comparing the developed electric signal with the reference electric signal to provide an error signal controlling the high gain device to determine the amount of energy fed to the motor. The motor speed control structure disclosed includes pulse producing structure for energizing the motor with pulses of electric energy and has fail safe features for use with vehicles.

United States Patent 1191 Kearns 1 Apr. 8, 1975 [76] Inventor:

[ 1 STRUCTURE FOR AND METHOD OF SURFACE CONDITION SENSING AND INDICATINGAND MOTOR SPEED CONTROL Robert W. Kearns, 9725 Lookout Pl.,Gaithersburg, Md. 20760 [22] Filed: Mar. 12, 1973 [2l] Appl. No.2340,557

Related US. Application Data [60] Division of Ser. No. 48,795, June 8,1970, Pat, No. 3,721,115, which is a continuation of Ser. No. 666,703,Sept. 11, 1967, abandoned.

s21 u.s.c|. ..318/33l;3l8/337;3l8/345 s11 1nt.C1. 1102p 5/06 [58]FieldofSearch ..3l8/33l,337,341,345,

Primary ExaminerRobert K. Schaefer Assistant E.\'aminer.|ohn .1.Feldhaus Attorney, Agent, or Firm-Whittemore, Hulbert & Belknap [571 IABSTRACT The condition of a surface is sensed by cyclically moving twomembers having engaged surfaces relative to each other, driving thesurfaces for only a portion of each cycle to set up a'threshold kineticenergy level in accordance with the friction between the engagedsurfaces, sensing the kinetic energy developed in one of the members dueto moving the members relative to each other, comparing the developedkinetic energy with the threshold kinetic energy and controlling thecyclic movement of the members in accordance with the relationshipbetween the kinetic energy threshold and the developed kinetic energy.The cyclic movement of the members is then used to provide a visualindication of the condition of one of the surfaces.

The structure for surface condition sensing and 'indicating includes apair of cyclically relatively movable members in surface-to-surfacefrictional engagement, means for driving the members relatively for aportion of a cycle of relative movement thereof, means preventingdriving of the members for the rest of the cycle of relative movementthereof to establish a threshold of kinetic energy in one of the membersnecessary to maintain relative movement between the members during theportion of the cycle in which they are not driven relatively, means tosense the relation between the kinetic energy of the one of said membersrelative to the threshold kinetic energy established, means for varyingthe time between cycles of driving the members relatively in accordancewith the relation between the established threshold of kinetic energyand the sensed kinetic energy of the one member and means for providinga visual indication of the relation between the kinetic energies. Themeans for controlling the cycle time includes means for immediatelystarting a new cycle of operation if the sensed .kinetic energy isgreater than the threshold kinetic energy established and for providinga predetermined dwell time between cycles of relative movement of themembers if the sensed kinetic energy level is below the establishedkinetic energy level. Structure is also disclosed for varying the dwelltime in accordance with the exact proportion between the establishedkinetic energy level and the sensed kinetic energy level in conjunctionwith particular structure for developing an electric signal proportionalto speed of an electric motor.

The particular structure for developing a signal proportional to motorspeed includes one or more additional commutator brushes provided inconjuction with the motor through which a signal is developed from themotor proportional to motor speed. The particular structure fordeveloping a signal proportional to motor speed is also disclosed inconjunction with a method of and means for motor speed control. Themethod of motor speed control includes driving an electric motor with anelectric signal, taking an electric signal from the motor itselfproportional to motor speed and controlling the signal electric siganlwith the signal proportional to motor speed. The structure disclosed forcontrolling the speed of a motor includes a source of reference electricsignal high gain structure for feeding electric energy to the motor, theparticular structure including a third commutator brush on the motor fordeveloping an electrical signal proportional to the speed of the motor,means for comparing the developed electric signal with the referenceelectric signal to provide an error signal controlling the high gaindevice to determine the amount of energy fed to the motor. The motorspeed control structure disclosed includes pulse producing structure forenergizing the motor with pulses of electric energy and has fail safefeatures for use with vehicles.

12 Claims, 10 Drawing Figures PATEHTEBAPR 8 1975 mm 2 III 3 FIG.7

A.C. T0 0.0. CONVERTER AUXILIARY CONTROL AUXILIARY H6 8 CONTROLAUXILIARY CONTROL AUXILIARY I H69 CONTROL I82 I84 [I74 SOURCE OF POWERI78 PULSES STRUCTURE FOR AND METHOD OF SURFACE CONDITION SENSING ANDINDICATING AND MOTOR SPEED CONTROL CROSS-REFERENCE TO RELATEDAPPLICATIONS This application is a division of application Ser. No.48,795, filed by applicant on June 8, I970, now U.S. Pat. No. 3,72l,l15, which application was a continuation of application Ser. No.666,703, filed Sept. II, 1967, now abandoned.

BACKGROUND OF THE INVENTION 1. Field of the Invention The inventionrelates to highway safety methods and structures and refers morespecifically to determining the condition of a highway surface or thelike and providing an indication thereof, particular structure forproviding a signal proportional to the speed of an electric motor fromthe motor itself, and a method of and structure for motor speed controlwith the particular structure.

2. Prior Art There is considerable emphasis today on highway safety. Asa result, automobile manufacturers and highway engineers are attemptingto improve the safety of both automobiles and highways. There are,however, many parameters of highway safety which are beyond the controlof automotive and highway engineers. One of the significant parametersinfluencing highway safety is weather conditions. Weather conditions mayproduce particularly dangerous highways due to the degree ofslipperiness of the road surface.

In the past, attempts have been made to determine the condition of aroad surface and to warn approaching motorists when the road surfacecondition is dangerous. Such attempts have often taken the form ofinstruments for measuring the dew point and temperature to determine theexistence of, for example, water or ice on a highway. However, suchdevices have not been the ultimate answer since highway surfaces may beslippery without water or ice thereon. For example, small granules ofsand distributed on the surface of a highway will seriously reduce thecoefficient of friction of the surface so that vehicle tires may slideon the road surface. Therefore, it is desirable to more exactly measurethe coefficient of friction or slipperiness of a road surface ratherthan specific conditions thereof, such as the presence of water or icethereon.

In addition, wherein motor speed control devices have been provided inthe past, they have generally included separate equipment, such astachometers to provide a feedback signal proportional to motor speed.Such additional equipment is expensive and not essential in motor speedcontrol apparatus.

Also, prior speed controls for electric motors have not usually beenfail safe. That is, they have not included structure for preventingoperation of the motor if the motor speed control circuit malfunctions.A fail safe motor control circuit is particularly desirable inconjunction with electrically driven automobiles and the like.

SUMMARY OF THE INVENTION The invention includes a structure for andmethod of sensing the condition of a surface, for example, a highwaysurface and providing a visual indication of the condition of thesurface. A means for and a method of varying the visual indication ofthe condition of the surface in accordance with the surface condition isalso provided.

The surface condition sensing structure includes an electric motorcircuit in which an additional brush is engaged with the commutatorwhich redistributes the current provided in the armature whereby asignal is available proportional to the speed of the motor which is partof the invention.

The motor speed signal developing circuit of the invention isparticularly useful in providing an efficient, inexpensive method of andcircuit for motor speed control in accordance with the invention. Themotor speed control circuit of the invention includes fail safestructure to prevent operation of a motor controlled by the motor speedcontrol circuit on failure of the motor speed control circuit.

DESCRIPTION or THE DRAWINGS FIG. 1 is a section view of structure forsurface condition sensing and indicating in accordance with the methodof the invention constructed in accordance with the invention.

FIG. 2 is a top view of the surface condition sensing structureillustrated in FIG. 1 taken in the direction of arrow 2 in FIG. 1.

FIG. 3 is a partial elevation view of the surface condition sensingstructure illustrated in FIG. 1 taken in the direction of arrow 3 inFIG. 1.

FIG. 4 is a schematic diagram of the electrical portion of the structurefor sensing surface conditions illustrated in FIGS. 1 through 3.

FIG. 5 is a schematic diagram of another embodiment of the electricalportion of the structure for sensing surface conditions illustrated inFIGS. 1 through 3.

FIG. 6 is a schematic diagram of structure for providing an electricalsignal proportional to motor speed constructed in accordance with theinvention in a motor speed control circuit for practicing the motorspeed control method of the invention.

FIGS. 7 and 8 are partly schematic, partly block diagrams ofmodifications of the motor speed control circuit illustrated in FIG. 6.

FIG. 9 is a partially schematic, partially block diagram of yet anothermodification of the motor speed control circuit illustrated in FIG. 6,wherein the motor is energized by pulses of electrical energy.

FIG. 10 is a detailed schematic diagram of one embodiment of the motorspeed control circuit illustrated in FIG. 9.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The structure 10 for sensingand indicating a surface condition illustrated in FIG. 1 includes a discmember 12 of a first material which is the material the surfacecondition of which it is desired to sense and indicate. For example, thematerial 12 may be material the same as a highway surface adjacent whichthe structure 10 is positioned. The surface of the material 12 and thesurface of the highway will then have the same coefficien-t of frictionor the same slipperiness under the same conditions.

The structure 10 further includes the movable member 14 having a surface16 in surface-to-surface engagement with the surface 18 of the disc 12connected to the arm 20 for rotation about the drive shaft 22 extendingfrom transmission 24 which is driven by the motor 26. The resilientmeans 28 is provided between the shaft 22 and the arm 20 for regulatingthe normal force with which the surface 16 engages the surface 18.

As shown best in FIG. 1, the material 12 is mounted at an angle a withrespect to the horizontal and is supported on the frame 30 which encasesthe transmission 24, motor 26 and the electrical portion 32 of thestructure 10. The indicating portion 34 of the structure l which, asshown, includes a sign 35 in front of lights 68 may also be enclosed bythe frame 30, as will be understood by those in the art.

A guard 36 of expanded metal is provided, as shown in FIG. 1,'to preventplacement of undesirable objects on the disc 12 which would give a falseindication of a surface condition of, for example, a highway adjacentthe structure 10. The diameter of the guard 36 in conjunction with theangle at which disc 12 is positioned with respect to the horizontal andthe angle at which the member 14 is positioned with respect to theradius of the disc 12, together with the extension of the member 14radially beyond the edge of disc 12, will maintain the surface of thedisc 12 substantially clean. Thus, on each revolution of the member 14on the disc 12, the disc 12 will be swept clean. Snow and other solidstending to. accumulate thereon will pass between the outer periphery ofthe disc ,12 and the guard 36. It is intended that the structure beplaced at a substantial height above the ground adjacent a highway tominimize the chance of tampering therewith and articles being placedthereon and to provide maximum visibility thereof.

The electrical portion 32 of the structure 10, shown best in FIG. 4,includes the motor 26 connected between a source of positive electricenergy 36 and ground 38 in series with the emitter collector circuit ofthe transistor 40. A cam 42 is secured to the transmission 24 forrotation at the speed of the motor 26. The cam 42 is mechanicallyconnected to the double throw switch 44. The movable contact 46 of theswitch 44 is connected through a resistor 48 to one side of thecapacitor 50. One fixed contact 52 of the switch 44 is connected toground, while the other fixed contact 54 of the switch 44 is connectedto the source of positive electric energy.

The circuit 32 further includes the potentiometer 58 having a resistor60 in series with a second resistor 62 connected between ground and theother side of the capacitor 50. The wiper arm 64 of potentiometer 58 isconnected directly to ground. A field effect transistor 66 having asource connected through resistor 64 to the source of positive electricenergy and to the base of the transistor 40, a drain connected directlyto ground and a gate connected directly to the junction between theresistor 62 and the other side of the capacitor 50 completes a controlloop in the circuit of the motor 26.

The circuit 32 further includes a plurality of lamps 68 connected inparallel with each other and in series with a source of alternatingelectric energy 70 and a Triac 72. As shown, the control electrode ofthe Triac is connected to the emitter-collector circuit of a transistor74. The emitter-collector circuit of the'transistor 74 is connected inseries between the source of positive electric energy and resistor 76.The resistor 76 is also connected to ground. The base of the transistor74 is connected through the resistor 78 to ground and to the drain of asecond field effect transistor 80. The second field effect transistor 80includes a source connected to the source of positive electric energyand a gate connected through a, resistor 82 to the gate of the fieldeffect transistor 66 and the junction between the resistor 62 and theother side of the capacitor 50, as shown best in FIG. 4. V

In overall operation of the structure 10, it is assumed that the cam 42is out of the 0 angle region so that the switch 44 is in the positionillustrated in FIG. 4. Any time that the cam 42 passes through the 0angle in its rotation with the motor 26, the movable contact 46 ofswitch 44 will be connected to the positive source of electric energythrough the contact 54. With the switch 44 in the position illustratedin FIG. 4, current will flow from the base of transistor 40 throughfield effect transistor 66 and'the resistors 60 and 62 in series toground.

The transistor 40 will therefore be on so that the motor 26 will bedriven and the capacitor 50 will be charging to a positive potential onthe right side thereof.

Also, at this time the field effect transistor 80 will be turned on toprovide a voltage on the base of the transistor 74, maintaining thetransistor 74 in an off condition. With transistor 74 off, the Triac 72is actuated by current through resistor 76, whereby the lights 68 areenergized through the power supply by Triac 72.

When the motor 26 rotates into the 6 angle, the contact 46 of switch 44engages the contact 54, whereby the positive voltage source is connectedto the left side of the capacitor 50. Then, because the capacitor 50cannot change its charge instantaneously a positive charge on the righthand side of the capacitor 50 equal to twice the positive voltage sourcewill be present. Such charge on the right side of thecapacitor 50.

will cause the field effect transistors 66 and to turn off.

The turning off of the field effect transistor 66 will turn off thetransistor 40 to stop driving of the motor 26. The turning off of thefield effect transistor 80 will cause conduction of the transistor 74 toplace the gate electrode of the Triac 72 at the positive voltage sourcelevel to turn off the Triac 72 and disconnect the lights 68 from thepower supply 70.

The field effect transistors 66 and 80 remain in the off condition untilthe capacitor 50 can discharge through a time constant, including thecapacitor 50 and.

the resistances 60, 62 and 48 in series. If prior to timing out of thetime constant the motor 26 turns sufficiently.

to move the cam 42 through the 0 angle, the switch 44 will return to theposition illustrated in FIG. 4 and the.

capacitor 50 will again start to charge, the field effect transistors 66and 80 will turn on and a new cycle of operation of the structure 10will begin.

In terms of the members 12 and 14, it will be understood that rotationof the motor 26 will rotate the member 14 in surface-to-surfaceengagement with the disc 12 to develop kinetic energy in the member 14.If during rotation of the motor 26, as the cam 24 moves into the 0angle, the kinetic energy in the member 14 is sufficient to move themember 14 through the 0 angle against the retarding action of thefrictional forces between the surfaces 16 and 18 to start a subsequentdriving cycle of the motor 26 and member 14, the lights 68 will stay onsubstantially constantly. If however, the condition of the surface 16 ofthe disc 12 is such as to provide a high coefficient of friction so thatlittle ki-v netic energy is developed in the member 14 during rotationthereof and high drag is present on the member 14 in the 6 angle, themember 14 will stop in the 0 angle some place and a subsequent cycle ofoperation of the structure 10 must await the discharging of thecapacitor 50 through the resistances 62, 60 and 48.

The time constant of the capacitor 50 and of resistances 60, 62 and 48may be considerable, that is, for example, ten minutes. It will,therefore, be understood that the lights 68 of the indicator 34 willilluminate the sign 35 substantially constantly when the surface 18 isof a condition such that the coefficient of friction thereof is so lowthat the member 14 will slide through the 0 angle. When the kineticenergy of the member 14 is not equal to the threshold level of kineticenergy determined by the 0 angle and the particular materials andstructure 10 so that the member 14 stops within the 0 angle during acycle of operation of the structure 10, the lights 68 will be outsubstantially all of the time. That is, for example, with the member 14making one revolution per second and with a time delay or dwell time often minutes, when the member stops in the 0 angle, the lights 68 wouldbe on only one six-hundredth of the time. Drivers observing thestructure 10 and particularly the indicator 34 thereof would thus bewarned of a surface condition on the highway matched by the surfacecondition of the disc 12 which provides a dangerously low coefficient offriction between the highway and automobile tires having substantiallythe same material composition as the member 14.

The circuit of FIG. 4 thus provides a slippery or nonslippery indicationto a driver as a warning. It would, however, be desirable if theindication were more qualitative. That is to say, it would be of moreinformation to a motorist if the length of time the indicator 34 wereilluminated were related to the degree of slipperiness of the roadsurface. Thus, if the road is slippery enough and the surface 18 is insuch a condition that the member 14 almost slips through the 0 angle, itwould be desirable to illuminate the indicator 34 for a longer period oftime than when the surface 18 is not slippery, has a high coefficient offriction and the kinetic energy developed in the member 14 isconsiderably below the threshold value which would allow the member 14to slip through the 0 angle. The circuit of FIG. 5 will provide suchoperation of the apparatus 10.

In the circuit of FIG. 5, the motor 26 is a direct current motor,including an armature connected to a commutator and including at leasttwo brushes 82 and 84 engaged with the commutator for passing a directcurrent motor driving signal through the armature of the motor 26. Withsuch a motor 26, a third brush 86 positioned on the commutator willprovide a signal proportional to the speed of the motor 26. In suchstructure, the motor 26 acts in the nature of a tachometer, wherein thesection of the armature between brushes 82 and 86 is rotated in a fixedmagnetic field to provide a signal proportional to the speed of rotationof the armature.

- In using a tachometer to develop a signal proportional to motor speedthe voltage developed is purely due to the rotation of the armature.However, when the motor 26 is used to provide a feedback signalrepresentative of the speed of the motor through an additionalcommutator brush 86, the signal at the brush is a function of bothcurrent through the motor and the motor speed. That is to say, that thevoltage across the motor armature is equal to the current through thearmature times the resistance of the armature plus the backelectromotive force in volts per radiance per second times the armatureangular velocity in radiance per second. Thus, when the speed of themotor 26 is low and the current times resistance component is large aspeed control signal based on the voltage across a portion of thearmature is in error. However, with the brush 86 placed close to theground brush 82, the current flowing therebetween is small so that thesignal output from the brush 86 is close to a true function of motorspeed.

The modified circuit 88, illustrated in FIG. 5, includes an additionalbrush on the commutator of motor 26 and the transistor 90 and having anemittercollector circuit connected between the brush 84 of the motor 26and a positive source of electric energy 92. The base of transistor 90is connected between the resistors 94 and 96 as illustrated. A secondtransistor 98 has its emitter collector circuit connected between theresistor 96 and ground and includes a base connected to one side of acapacitor 100. The base of the transistor 98 is also connected throughthe resistor 102, the resistance 104 and wiper arm 108 to the source ofpositive electrical energy 92 and the other end of resistor 94 as shown.

The left side of capacitor is connected through a resistance 110 to thesource of positive electric energy and to the movable center contact 112of switch 114. Thus, when the cam 128 driven by motor 26 is outside ofthe 0 angle, the contact 112 of switch 114 is in engagement with thedead contact 116 of the switch 114 and when the cam 126 is in the-0angle, the contact 112 of the switch 114 is in engagement with thegrounded contact 118 of the switch 114.

The circuit of FIG. 5 is completed by the transistor 120 having agrounded collector 120 and an emitter connected directly to the leftside of the capacitor 100. The base of transistor 120 is connectedthrough a resistor 122 and a filter network including a diode 124 and acapacitor 126 to the added brush 86 on the commutator of the motor 26.

In operation of the circuit of FIG. 5, when the motor 26 is rotatingslowly, that is due to a high torque load thereon because of highfriction between the surfaces 18 and 16 of members 12 and 14, a smallfeedback voltage will be fed from the third brush 86 on the commutatorof motor 26 through the diode 124 and resistor 122 across capacitor 126to the base of the transistor 120. The small voltage will not besufficient to turn the transistor 120 on. Therefore, the junctionbetween the resistor 110 and capacitor 100 will rise to the positivepotential of the source of positive electric energy to charge thecapacitor 100 positive on the left side and negative on the right side.The transistor 98 will thus be biased on and the transistor 90 willtherefore also be on to provide driving current through the motor 26.

When the cam 128 is rotated into the 0 angle, the contact 112 of theswitch 114 is moved from the dead contact 116 to the grounded contact118. The left side of the capacitor 100 is thus grounded so that adifference in potential of the value of the positive source of electricenergy will appear across the capacitor 100. The transistor 93 is thuscaused to turn off and will turn off the transistor 90 to preventdriving of the motor 26. The time delay will be shorter since thecapacitor is not fully charged.

" The transistor 9.8,:will remain in the turned off condition until thecharge-on the capacitor 100 has been drained off through the resistancecapacitance time constant provided by the resistors 102, 104 and 110 andthe capacitor 100. This time constant can be changed by the position ofthe potentiometer wiper arm 108. When the transistor 98 is turned on,the lights 68 which may be connected as before to the right hand side ofthe capacitor 100 may be energized through a circuit, such as the bottomcircuit of FIG. 4, to indicate a non-slippery surface by blinking onlyat large intervals.

Assume then that the surface 18 of member 12 is slippery, as when ice orwater have collected thereon to substantially reduce the coefficientfriction between the surfaces 16 and 18 and to increase the keneticenergy in the movable member 14 and the speed of the motor 26, thefeedback voltage from the third brush 86 on the commutator of the motor26 will be sufficient to turn on the transistor 120 so that theresistance offered by the transistor 120 and the resistor 110 will forma voltage divider to divide the voltage of the source of positiveelectric energy. The voltage at the junction between the resistor 110and the left hand side of the capacitor 100 will then be determined bythe feedback voltage from the motor 26 due to the degree of conduc- Ition of the transistor 120. That is to say, for example, if the motor 26is running very fast, the transistor 120 will be turned full on and theleft hand side of the capacitor 100 will be substantially at ground.

When the cam 128 passes through the angle, the switch 114 again placesthe left hand side of the capacitor 100 at ground through the contact118. The charge on .the capacitor 100 will then go from some positivepotential to which it has been allowed to charge with transistor 120 onto ground on the left side during a time constant, again determined bythe resistors 102, I04 and 110 and the capacitor 100. The transistors 98and 90 will again be turned off during this period and the motor 26 willnot be driven and the lights will not be energized.

Now, as the speed of the motor 26 is increased, that is as the surface18 becomes more slippery, the initial charge on the capacitor 100 as thecam goes into the 0 angle will become smaller and the time that thetransistors 98 and 90 are turned off will become progressively lessuntil the lights 68 are energized substantially all of the time. Thus,the circuit of FIG. will cause the lights 68 to be energized exactly inaccordance with the speed of the motor 26 and the condition of thesurface 18.

As indicated above, the including of an additional brush on thecommutator of motor 28 will provide a signal which is proportional tomotor speed. In FIG. 6 the feedback voltage provided from a third brush142 on an electric motor is used to provide motor speed control.

In the circuit of FIG. 6, the resistors 130 and 132 provide a comparisonbetween the desired speed represented by the position of the wiper arm134 on the resistor 136 of potentiometer 138 with the feedback voltagefrom the motor 140 through the additional brush 142 on the motorcommutator. The feedback signal through the resistor 132 is of a signopposite of the signal through the resistor 130. The difference betweenthese two signals to provide a control signal may be very small if theamplifier 144 has a high gain or in other words is a very large transferfunction. The current through resistors 130 and 132 would in suchstructure be substantially equal when the motor is running at theregulated speed therefor.

When the speed of rotation of the motor 140 is reduced, as for exampleby a heavy load, the feedback signal would be reduced to provide anincreased signal through the amplifier 144 to drive the motor 140 harderand thus increase the speed thereof to being it back to the regulatedspeed. Similarly, when the motor speed is too high, the error signalprovided the amplifier 144 will be such as to slow the motor down tobeing it back to the regulated speed.

The feedback signal from the motor 140 will be a complex signal havingboth an alternating and direct component due to the usual commutatorsructure. If it is desired to operate with only the alternating feedbacksignal, a circuit, such as illustrated in FIG. 7 may be used, wherein apair of additional brushes 148 and 150 are provided on the commutator ofthe motor 146 which brushes are connected to the primary winding 152 oftransformer 154 having the'secondary winding 155. The purely alternatingfeedback signal component is then passed through the alternating todirect signal converter to provide operation of the speed control, as inFIG. 6.

Also, as indicated in FIG. 8, by varying the location of a plurality ofauxiliary brushes 158, 160, 162 and 164 on motor 166 different magnitudefeedback signals, each porportional to motor speed, may be tapped fromthe motor 166. These feedback voltages may as indicated be used toenergize auxiliary control units which would then respond to the speedof rotation of the motor 166.

Considering motor speed control through the use of auxiliary brushes onthe commutator of electrical motors further, it will be understood thatthe most efficient way of controlling a direct current motor is withpulses of electrical energy. With such speed controls, transistors arenormally used as switching devices. One such motor speed control 170 isillustrated generally in FIG. 9, wherein the motor 172 is controlled bypulses from the source of power pulses 174 in accordance with thevoltage comparison between the voltage tapped from potentiometer 176 bywiper arm 178 and the electric signal tapped from the motor 172 throughthe brush 180 across the resistors 182 and 184. These pulsed, transistorcontrolled systems are particularly efficient voltage drop across thetransistors supplying the current is small and when the current throughthe motor,

is small, the voltage drop across the controlling transistors is highand the voltage drop across the motor is small. Consequently the powerloss in such systems is limited to a very short time in which thetransistor is switching.

In addition, it will be remembered that the motor is basically anintegrator in conjunction with such systems. Consequently the powerpulses for driving the motor 172 are smoothed by the motor. If thefrequency is high enough. it is then difficult to detect that the motoris not drawing power and rotating continuously. Due to this smoothingaction of the motor, the signal generated at the third brush 180 isgoing to be smooth. Consequently, by using pulse width modulation tovary the power to the motor efficiently and by using a third brush toobtain effective tachometer feedback, an effi-.

cient well regulated speed control 170 is achieved.

By operating the source of power pulses at as low a frequency asreasonable to obtain smooth operation, power loss in the system isminimized. By operating the source of power pulses or oscillator at neara constant frequency, smooth operation of the speed control is achievedover its operating range. Thus, at start-up, the motor initially turnsslowly and is receiving power pulses at a high pulse per revolutionrate. At high speed, the motor receives power pulses at a low pulse perrevolution rate which enhances the efficiency of the speed control asdescribed above. At high speed, the high momentum of thesystem allowssmooth operation with power pulses at a low effective pulse rate.

A pulse controlled motor speed control 186 having fail safe features isillustrated in more detail in FIG. 10. In the motor speed controlstructure of FIG. 10, the motor 188 is provided with the usualcommutator brushes 190 and 192 and with the third commutator brush 194for again providing a signal proportional to motor speed. The motor 188is illustrated as having a series field 196 although the indicated speedcontrol could be used equally well with a motor having a permanentmagnet field. The diode 200 is a smoothing diode which provides acurrentpath with the transistor 202 turned off.

The feedback signal from the motor 188 is again passed through thefilter and current limiting circuit, including the diode 204 andcapacitor 206 and the resistance 208. Again, when the motor 188 isrotated at a sufficient speed, the transistor2l0 will be turned on toprovide a current flow through resistor 212 proportional to thefeed-back signal from the motor 188 for comparison with theelectricsignal 214 tapped from the resistor 216 of the potentiometer 218 havinga wiper arm 220. The difference in the electrical signals through theresistors 212 and 214 is passed through the high gain transfer circuit222 to again charge the left side of capacitor 224 positive an amountdepending on the speed of the motor 188. It will be noted that thecapacitor is charged while the motor is coasting so that the charge onthe capacitor is more indicative of purely motor speed. That is to say,it is not affected by a power current burst.

The square wave oscillator 226 is provided to return the capacitor 224to ground periodically, causing a voltage change on the right hand-sideof the capacitor 224 sufficient to cause conduction of the field effecttransistor226 having a gate electrode connected to the right side ofcapacitor 224 and having source and drain electrodes connected to themovable contact of switch 228 and through resistor 230 to the wiper arm232 of potentiometer 234. The field effect transistor 226 will remainturned on for a time determined by the time constant of the capacitor224 and the resistance 236 and the resistor 238 of the potentiometer234. As

shown, the wiper arm 232 of the potentiometer 234 is connected back tothe source of positive electric energy 240.

When the field effect transistor 226 is turned on, the transistor 242and transistor 202 connected as shown are turned on to provide currentthrough the transistor 202' and the contacts 228 and 244 of the switch246 to energize the motor 188. The pulse width of the motor energizingpulse through the switch 246 may be regulated by the position of thepotentiometer wiper arm 232 and motor speed control may be effected asbefore.

It will however be noted that in the motor speed control circuit of FIG.10 that a pulse of motor energy is provided during the power pulse whichaccompanies a control pulse, wherein in the motor speed control circuitof FIG. 5 the control pulse kept the power to the motor off. The circuitof FIG. 10 thus has an advantage in the event that the control is usedto drive a vehicle since a loss of control pulses would turn thevehicles power off. That is the control circuit of FIG. 10 is fail safe.Should the control circuit of FIG. 10 fail by, for example, having thefield effect transistor 226 or the transistors 242 or 202 short, thealternating current amplifier 248 would no longer receive pulses fromthe transistor 202 through the coupling capacitor 250 and would causethe relay 252 to open the switch 246.-

While one embodiment of the present invention and modifications thereofhave been disclosed in detail, it will be understood that otherembodiments and modifications are contemplated by the inventor. It istherefore the intention to include all embodiments and modifications asare defined by the appended claim within the scope of the invention.

What I claim as my invention is:

1. An electric motor including a commutator and an armature having atleast two commutator brushes for conducting current to the armature, anadditional commutator brush for simultaneously obtaining an electricsignal from the motor which is a function of motor rotation, means forsupplying a regulating reference signal, high gain electric motor drivemeans including means for providing driving pulses for the motor, andmeans for comparing the signal from the motor and the reference signalto provide a motor speed regulating signal to the high gain drive means.

2. Structure as set forth in claim 1 and further including a pluralityof additional commutator brushes for providing a plurality of additionalsignals proportional to motor rotation for auxiliary control functions.

3. Structure as set forth in claim 1 and further including a secondadditional commutator brush, a transformer primary winding connectedbetween the additional commutator brushes and a transformer secondarywinding operably associated with the transformer primary winding forproducing an alternating current component of the obtained electricsignal from the motor.

4. Structure as set forth in claim 3 and further including analternating current to direct current converter connected to thesecondary winding of the transformer to provide a direct currentelectric signal proportional to the alternating current component of theobtained electric signal from the motor.

5. Structure as set forth in claim 1 and further including meansoperably associated with the means for obtaining an electric signal fromthe motor and the motor for making the motor speed regulating signalfail safe.

6. Structure as set forth in claim 5 wherein the means for making themotor speed regulating signal fail safe includes means for energizingthe motor only in response to driving pulses.

7. Structure as set forth in claim 1 wherein the additional brush islocated so as to control the polarity of the obtained electric signalfrom the motor.

8. In combination with a control system utilizing an electric motorwhich contains a brush-type commutator assembly including at least twobrushes for deriving a first electric signal, a motor speed detectorcomprising a single additional brush slidably engaging the commutatorassembly for deriving a second electric signal simultaneously with saidfirst electric signal, capacitor means connected to receive the secondelectric signal and switch means connected to the capacitor meansoperable to periodically cause discharge of the capacitor means forconditioning the derived second electric signal to control an operationin response to the rate of rotation of the motor.

9. Structure as set forth in claim 8 wherein the operation controlled isthe angular rate of the electric motor.

10. Structure as set forth in claim 8 wherein the additional brush meansis located such that the derived signal is of one polarity, means forproducing a command signal of the other polarity and the means forcontrolling an operation in response to the rotation of the means tomodulate the pulses of power to actuate said motor includes means forvarying at least one of the amplitude and width of the pulses.

1. An electric motor including a commutator and an armature having atleast two commutator brushes for conducting current to the armature, anadditional commutator brush for simultaneously obtaining an electricsignal from the motor which is a function of motor rotation, means forsupplying a regulating reference signal, high gain electric motor drivemeans including means for providing driving pulses for the motor, andmeans for comparing the signal from the motor and the reference signalto provide a motor speed regulating signal to the high gain drive means.2. Structure as set forth in claim 1 and further including a pluralityof additional commutator brushes for providing a plurality of additionalsignals proportional to motor rotation for auxiliary control functions.3. Structure as set forth in claim 1 and further including a secondadditional commutator brush, a transformer primary winding connectedbetween the additional commutator brushes and a transformer secondarywinding operably associated with the transformer primary winding forproducing an alternating current component of the obtained electricsignal from the motor.
 4. Structure as set forth in claim 3 and furtherincluding an alternating current to direct current converter connectedto the secondary winding of the transformer to provide a direct currentelectric signal proportional to the alternating current component of theobtained electric signal from the motor.
 5. Structure as set forth inclaim 1 and further including means operably associated with the meansfor obtaining an electric signal from the motor and the motor for makingthe motor speed regulating signal fail safe.
 6. Structure as set forthin claim 5 wherein the means for making the motor speed regulatingsignal fail safe includes means for energizing the motor only inresponse to driving pulses.
 7. Structure as set forth in claim 1 whereinthe additional brush is located so as to control the polarity of theobtained electric signal from the motor.
 8. In combination with acontrol system utilizing an electric motor which contains a brush-typecommutator assembly including at least two brushes for deriving a firstelectric signal, a motor speed detector comprising a single additionalbrush slidably engaging the commutator assembly for deriving a secondelectric signal simultaneously with said first electric signal,capacitor means connected to receive the second electric signal andswitch means connected to the capacitor means operable to periodicallycause discharge of the capacitor means for conditioning the derivedsecond electric signal to control an operation in response to the rateof rotation of the motor.
 9. Structure as set forth in claim 8 whereinthe operation controlled is the angular rate of the electric motor. 10.Structure as set forth in claim 8 wherein the additional brush means islocated such that the derived signal is of one polarity, means forproducing a command signal of the other polarity and the means forcontrolling an operation in response to the rotation of the motorincludes comparison means for deriving a signal related to thedifference between the command and conditioned brush signals and meansto condition said signal associated with the difference between thecommand and conditioned brush signals to actuate said motor. 11.Structure as set forth in claim 10 wherein the means to condition thesignal associated with the difference between the command andconditioned brush signals includes means for modulating pulses of powerto actuate said motor.
 12. Structure as set forth in claim 11 whereinthe means to modulate the pulses of power to actuate said motor includesmeans for varying at least one of the amplitude and width of the pulses.